2of3In this Thursday, June 28, 2012 photo, embers of the Free Syrian Army are seen in a neighborhood of Damascus, Syria. Much of the violence that has gripped Syria has been sanctioned by the government to crush dissent. But rebel fighters are launching increasingly deadly attacks on regime targets, and several huge suicide bombings this year suggest al-Qaida or other extremists are joining the battle. A bomb blast rocked central Damascus on Thursday near a busy market and the country's main justice complex, wounding at least three people and sending a cloud of black smoke into the air. (AP Photo)Photo: Anonymous

3of3Secretary of State Hillary Clinton met with Russian Foreign Minister Sergey Lavrov in St. Petersburg on the eve of a Geneva summit on the Syria crisis.Photo: HARAZ N. GHANBARI

GENEVA - The top U.S. and Russian diplomats failed to bridge critical differences about Syria on Friday during talks in Russia, leaving prospects uncertain for a high-level international "action group" scheduled to gather Saturday in Geneva.

Secretary of State Hillary Rodham Clinton attempted to persuade Russian Foreign Minister Sergei Lavrov that world powers need to take a more assertive role in bringing about a "political transition" to end the raging violence in Syria.

U.S. officials say that, as part of any transition, Syrian President Bashar Assad must go. But Russia has insisted that outside nations cannot force out Moscow's longtime ally and that Syrians must decide who leads them without external interference.

Friday's encounter in St. Petersburg apparently did not alter fundamental differences about how to end the violence in Syria.

A senior administration official said the two diplomats had "serious discussions on all areas of difficulty" on Syria, but that important gaps remained.

Nevertheless, U.S. officials have concluded that the Saturday meeting - meant to salvage U.N. special envoy Kofi Annan's faltering peace plan and hammer out a transition blueprint for Syria - may still be productive, the official said.

Russia's support for any U.N.-backed transition plan for Syria is crucial because Moscow is a veto-wielding member of the Security Council.

On Friday, Syria's opposition reported the deadliest 24-hour period so far and said rebel fighters had seized two Syrian generals, one of them the highest-ranking officer to fall into insurgent hands.

Tallies by Syrian opposition groups that track casualties reported Friday that the previous day's death toll had reached 190 from violence scattered in towns and cities throughout the country.

The largest number was concentrated in the Damascus suburb of Douma, an insurgent enclave.